It is known to prepare thermoplastic elastomeric copolyetheresters, which are essentially linear, by reacting together a mixture of a dicarboxylic acid (or its ester), a long chain polymeric glycol, and a low molecular weight diol in suitable proportions. The product is a segmented block copolyetherester composed both of long chain ester units, which are those segments of the polymer chain derived from the esterification of the long chain glycol with the dicarboxylic acid, and short chain ester units derived from the esterification of the low molecular weight diol with the dicarboxylic acid. In a specific embodiment copolyetherester elastomers are prepared by copolymerization of dimethyl terephthalate (DMT), butanediol, and poly(tetramethylene ether)glycol (PTMEG). The polyester units of DMT and butanediol form a high-melting hard segment in the block copolyetherester, while the long chain ester units provide high elongation to the segmented copolyetherester.
These copolyetheresters can be prepared by known procedures to provide elastomers having good tensile strength, tear strength, abrasion resistance, etc., but their hardness and their cost has limited their market penetration. Accordingly, there has existed a need for a means of lowering the hardness and the cost of existing copolyetherester elastomers, but without loss of its most important physical properties, particularly toughness. Attempts to soften the copolyetherester by addition of increased amounts of PTMEG have produced unfavorable side effects in that the melting point and elastomeric properties of the copolyetherester have been affected adversely and the cost has been increased. Attempts to soften the polymer by the addition of plasticizers of low or intermediate molecular weight which are structurally similar, e.g., polyester or polyethers, has led to similar adverse results. There is need for a cheaper substitute additive which can be blended with the copolyetherester to soften it but without adversely affecting its physical properties.